The invention concerns a take-out leading roll, spreader roll, or equivalent for a web-like material, which roll comprises a non-revolving roll axle and a roll mantle journalled revolvingly by means of bearings on said roll axle, and which roll can be bent to the shape of the desired arc.
Take-out leading rolls and spreader rolls have been formed most commonly so that they have a continuous axle and a roll mantle fitted on the axle, which roll mantle is again composed of a number of parts. The take-out leading roll can be made to be curved to the desired shape by shifting the outer journalling points of the roll mantle in the radial direction, in which connection the mantle forms an arc or a broken line. As a rule, each of the mantle parts is journalled separately on the axle, in which case the arrangement comprises a number of bearings. The conventional solutions involve a number of problems and drawbacks, which are, among other things, problems of journalling of the roll and peaks of heat produced by the journalling in the paper web. The making of the mantle of a number of parts may also constitute a considerable problem, because the gaps between the parts may mark the paper web and because the arc form of the roll is not optimal, but the line of shape of the roll is shaped as a broken line. Further, owing to the metallic roll mantle, problems of corrosion may arise. One such prior-art spreader roll is described, for example, in the U.S. Pat. No. 4,692,971. Attempts have been made to provide an improvement over such a prior-art spreader roll, for example, so that a coating layer of a resilient material has been fitted onto the metal mantle consisting of a number of parts, the objective of this arrangement being in particular to provide an improvement concerning the problem of marking of the paper web and concerning optimization of the arc form of the roll. However, the journalling system of the roll is similar to that described above, and, thus, also the problems related to the journalling are unchanged. Such a spreader roll is described, for example, in the Canadian Patent No. 766,843.
Earlier, attempts have been made to find a solution for the problem arising from a roll mantle consisting of a number of parts also so that, as the roll mantle, a continuous metal tube mantle has been used which has been provided with xe2x80x9ccutsxe2x80x9d, i.e. into which slots have been formed in order to facilitate the bending of the roll mantle. This construction, however, causes its own problems, one remarkable one of said problems being the fact that, owing to its construction, the roll mantle becomes quite slack, i.e. excessively readily bending. In such a case, the roll mantle concerned must be supported on the roll axle by means of bearings at a number of points, for which reason the problems described above and arising from the journalling remain unchanged. Also, the cost of manufacture of the roll mantle is relatively high because of the mode of manufacture.
The object of the present invention is to provide a novel construction of a take-out leading roll, spreader roll or equivalent, by whose means the problems related to the prior art described above are avoided. In view of achieving the objectives of the invention, the invention is mainly characterized in that the roll mantle is a continuous, tubular mantle, and that the roll axle consists of three parts linked with one another, i.e. of two end parts and of a middle part, which are pivotal in relation to one another for the purpose of bending the roll mantle.
By means of the invention, quite a considerable advantage is achieved over the prior art, and of the advantages obtainable by means of the invention, for example, the following should be stated. Owing to the construction in accordance with the invention, in the roll it is possible to use a mantle consisting of one part. As the material of the mantle, it is favourably possible to use a composite material, in which case the lowest natural frequencies of the roll can be raised to such a high level that a roll mantle supported exclusively at the ends can be used as the construction. In such a case the problems of heat arising from journalling, related to the prior art, can be avoided. When a fully continuous roll mantle with no gaps is used, all problems of marking of the paper web can also be avoided. When a composite material is used as the material of the roll mantle, all problems of corrosion can also be avoided. The further advantages and characteristic features of the invention come out from the following detailed description of the invention.